Conventionally, a medical device such as an infusion bag or a tube port is generally manufactured using soft polyvinyl chloride containing a plasticizer. The soft polyvinyl chloride has excellent flexibility, heat resistance, strength, or the like, as well as high kink stability or a tube.
Since the soft polyvinyl chloride has a chlorine atom in a main chain, a problem of easily generating dioxin during discarding and incinerating the soft polyvinyl chloride has been encountered. Also, a butyric acid ester-based plasticizer such as dioctyl butyrate to be added for the purpose of softening may be occasionally eluted into a medical infusion, in turn seriously becoming an environmental hormone.
In recent years, a medical device using polypropylene as a main substance, instead of such soft polyvinyl chloride, has been developed.
Although polypropylene has excellent heat resistance, polypropylene has a high possibility of being brittle in a low temperature environment. Thus, when a medical infusion bag made of polypropylene is used in a low temperature environment, it encounters a problem due to poor cold resistance of polypropylene such as tearing of the bag or the like. Further, polypropylene is often provided with an additive such as an antioxidant in order to prevent deterioration. For this reason, even in a case of using polypropylene, as with the case of using soft polyvinyl chloride, the additive into a medical infusion may be eluted.
As a substance to be used instead of polypropylene, polyethylene has been attracting attention. Polyethylene shows favorable cold resistance and may reduce the amount of additive required to be added polyethylene. Therefore, components eluted into a medical infusion are decreased. In addition, since polyethylene is inexpensive, it is possible to reduce production costs.
However, polyethylene typically has a heat resistant temperature of about 110° C., thus showing relatively lower heat resistance than polypropylene. For instance, for a medical infusion bag, since a medical infusion is disinfected (that is, sterilized) at a high temperature of 121° C. after filling the bag with the medical infusion, it requires improvement of heat resistance of polyethylene in order to manufacture the bag using polyethylene.
Polyethylene capable of withstanding high pressure steam sterilization at 121° C. has been recently developed and attracted attention as a medical infusion bag material.
When filling the medical infusion bag with the medical infusion, in general, a body of the bag storing the medical infusion therein has a tube, a so-called tube port, welded thereto and the medical infusion is fed into the bag body through the tube.
After feeding the medical infusion, a connector such as a twist-off spike port which is fluid-tight using a membrane is introduced into a front end of the tube, the tube is closed using a cap, and then high pressure steam sterilization is performed. Further, dripping is generally performed by piercing the connector with a needle mounted on the front end of a medical infusion line.
Accordingly, since the high pressure steam sterilization is executed while the tube is welded on the body of the medical infusion bag, the tube also requires excellent heat resistance. In addition, a contact part between the bag body and the tube, a contact part between the tube and the connector, or the like should be closely, that is, fluid-tightly, adhered.
With respect to the tube, for example, Patent Document 1 discloses a medical tube provided with three layers, including an outer layer made of soft polyvinyl chloride or a polyurethane-based copolymer as a main component, an intermediate layer made of chlorinated polyethylene or a maleic acid-based copolymer as a main component, and an inner layer made of polyethylene or ethylene and an α-olefin copolymer as a main component.
Further, Patent Document 2 discloses a multi-layer tube including an outer layer, an intermediate layer and an inner layer. In particular, the multi-layer tube is described to have the inner or outer layer which includes a composition of 85% of a three-component mixture containing polypropylene, a copolymer of ethylene and acrylic acid ester and a styrene-ethylene-butylene-styrene block copolymer, and 15% of a copolymer of ethylene and propylene.